Terminal structures for valve tubes



June 9, 1959 c. KIRKA TERMINAL STRUCTURES FOR VALVE TUBES Filed June 5,'1956 IN VEN TOR.

ATTORNEYS A K m R m R E M E H c II Twwwm i m II W it u; m. a a 2 UnitedStates Patent TERMINAL STRUCTURES FOR VALVE TUBES 'Chester Kirka,Stratford, Comm, assignor to Machlett Laboratories, Incorporated,Springdale, Conn., a corporation of Connecticut Application June 5,1956, Serial No. 589,413

3 Claims. (Cl. 315-58) This invention relates to electron dischargedevices and has particular reference to improved thermionic valve tubessuch as used in the power supply circuits for X-ray tubes.

Thermionic'valve tubes of the type referred to herein are generallyhigh-voltage half-Wave rectifier tubes which are used in X-rayapparatus, and which are intended for oil-immersed operation. In suchtubes it is desirable to provide filaments which function at maximumefiiciency with minimum power loss. It is particularly desirable toobtain high power output without the necessity of disposing of excessheat generated by lost power. To accomplish this, modern tubes of thepresently described type are provided with filaments of thoriatedtungsten or equivalent high emission material which requires relativelylow filament voltage and power to attain a desired amount of emission.Thoriated tungsten filaments are also desirable because they may, byappropriate design considerations, be made to have considerably longerlife than pure tungsten filaments.

Unfortunately, existing X-ray equipment is designed in most cases tosupply higher voltages to tube filaments becauseold style tubes requiredhigher voltages for op- 'eration of ordinary tungsten filaments. Thus,it has generally been ditficult to replace old-style tubes with improvedthoriated tungsten filament valve tubes without alteration of thefilament supply circuits.

Accordingly, it is a primary object of the present invention to providemeans whereby a valve tube having a filament requiring relatively lowoperating voltage may be used in circuitry which supplies relativelyhigh voltage.

Another object is to provide novel means in a valve tube whereby avoltage dropping resistance is included in the filament circuit of thetube for permitting a normally low voltage filament to be operated fromrelatively high voltage sources.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, in which Fig. 1 is an elevational view partly in sectionillustrating a preferred embodiment of the invention;

Fig. 2 is an end view of the tube shown in Fig. l; and

Fig. 3 is a fragmentary elevational view of the end of the tube shown inFig. 1, illustrating a modification in the terminal structure.

The present invention is used primarily in connection with a valve tubewhich is supported in position of use by means connected to the anode ofthe tube or to any portion of the tube other than the extreme endthrough which extend the filament leads. The invention resides in theprovision of flexible terminals which are connected directly to thefilament leads and which comprise high resistance wires of the lengthnecessary to reduce the voltage at the filament to the required level.The terminals are interchangeable with low resistance wires 2,890,385Patented June 9, 1959 "ice when it is desired to operate the filament atrelatively low normal voltages or after appropriate adjustments havebeen made in the relatively high voltage circuitry. Referring moreparticularly to Fig. 1, there is shown a tube which comprises a glassenvelope having a cylin drical central portion 10 and end portions 11and 12 of reduced diameter. Within end portion 11 is means forsupporting a tubular anode 13 which extends longitudinally within theenlarged central portion 10. Enclosing the end of envelope portion 11 isa dielectric cap 14 the base of which carries an anode terminal 15 whichis electrically connected to the anode 13. The cap 14 is rigidly affixedto the envelope and the terminal 15 is connected to an anode lead 13awithin the cap 14.

The opposite end of the envelope is provided with a reentrant portion 16which terminates in a stem press 17. Two spaced relatively rigidfilament supports 18 and 19 extend through the stem press 17, and to theinner end of each support is fixed a respective end of a catenary typefilament 20-, the central portion of the filament being supported by oneend of a third support 21 which has its opposed end fixedly mounted inthe stem press 17.

A shield 22 is mounted over the stem press 17 and adjacent portions ofthe filament supports to protect them from electron bombardment.

The outer ends of filament supports 18 and 19 termi nate slightly beyondthe stem press 17 and within the recess formed by the reentrant portion16, and to the end of each support 18 and 19 is fixed one end ofrespective flexible leads 23 and 24, which leads extend outwardly of therecess.

In accordance with the present invention, the filament 20 is designedfor optimum operation when it receives relatively low voltages such, forexample, as six volts. To permit the tubes to be used in equipment whichsupplies to the filament higher voltages such as ten volts, for example,means is provided at the tube for reducing the voltage between the powersupply of the equipment and the filament. This means comprises a pair ofvoltage dropping resistors 25 and 26 which are secured to the respectivefilament leads 23 and 24 and which are formed of high resistance wire.

Leads 23 and 24 extend through respective eyelets 27 and 28 in a deck 29which is adapted to close the recess formed by the reentrant portion 16of the envelope, the inner peripheral edge of the deck being held uponthe annular end of the envelope structure by the leads 23 and 24 whichare pulled through the eyelets tight enough to hold the deck in placeand are then soldered to the eyelets.

Also soldered, screwed, riveted or otherwise secured to the eyelets 27and 28 are respective substantially L-shaped lugs 30 and 31 to which areconnected ends of the respective resistors 25 and 26. The opposed endsof the resistors carry terminals 32 and 33 which are adapted to beplugged into the power supply circuit of the equipment with which thetube is to be used.

When this is done, the voltage applied to the terminals 32 and 33divides, a portion of the voltage being expended at the resistors 25 and26. Since the resistors are in series with the filament 20, the balanceof the voltage is expended at the filament to raise the filament to itsnormal operating temperature. In this way a thoriated tungsten filamentnormally operable at six volts, for example, may be used in a powersupply circuit which provides higher voltage, such as ten volts, as isrequired with conventional tungsten filaments.

Should the power supply circuit later be revised to supply six volts,the tube can then be used in the installation by merely removing thehigh resistance wires 25 and 26 and replacing them with the lowresistance y 3 wires 34 and 35 shown in Fig. 3, thus allowing thefilainent 20 to heat to its normal operating temperatures.

While the high resistance wires 25 and 26 are preferably soldered to thelugs 30 and 31, it will be apparent that they. maybe secured to the endsof the filament leads 23 and 24 by any other suitable means whichprovides'satisfa'ctory electrical conductivity between the leads and thewires. When a soldered connection is used," however, it. is a simpleoperation to snip off the high resistance wires at the solder connectionwith the lugs .and then solder low resistance wires in their place."Since the tube is preferably supported in position of use by the'anodeterminal 15, the cathode terminals need not'be rigid. This allows thewires to extend freely from the filament leads. However, to preventaccidental "shorting should one of the leads 23 or 24 beinadvertentlyloose and movable, the leads are provided with sleeves 36and 37 made preferably of a knitted dielectric fabric'material. At leastone of the high resistance wires 25'and 26, and also at least one of thelow resistance wires 34 and 35, are likewise covered with dielectricsleeves 38 or 39 respectively to prevent shorting.

From the foregoing description it will be apparent that all of theobjects of this invention have been accompli'shed by the provision ofnovel means for supplying valve'tubes which are supported at locationsother than the cathode ends thereof in various installations whichsupply different filament voltages to the tubes. It'will "also beapparent that various modifications an'dfchanges within the scope ofthis invention may be made by those skilled in the art; Therefore, allmatter shown and described should be interpreted as illustrative and'not in a limiting sense.

I claim:

l. A valve tube comprising a vacuum envelope having a' reentrant'portionat one end extending for a substantial distance into' the envelope andterminating in a stem'press and forming a central cavity in that end ofthe tube exteriorlyof the vacuumized portion of the envelope, a filamentin the vacuumized portion of the envelope, a pair of leads connectedwith the filament and extending outwardly of the envelope through thestem press into the cavity, an apertured dielectric deck located on theend of the envelope spanning the cavity, a pair of electricallyconductive members on the deck to which the outer'ends of the leads areconnected, a pair of metal lugs secured to and extending outwardly fromthe respective conductive members, and means carried by and forming partof the tube for connecting the filament to a source of power comprisinga pair of conductive elements of selected electrical resistancecharacteristics having one end connected to the respective lugs, theconductive elements being freely suspended from the lugsand having theirother ends adapted for connection to electrical means external of thetube.

2. A valve tube comprising a vacuum envelope having a reentrant portionat one end extending fora substantial distance into the envelope andterminating in a stem press and forming a central cavity in that end ofthe tube exteriorly of the vacuumized portion of the envelope, afilament in the vacuumized portion of the envelope, a pair of leadsconnected with the filament and extending outwardly of the envelopethrough the stem press into the cavity, a dielectric deck located on theend of the envelope and spanning the cavity, a pair of electricallyconductive members on the deck and to which the cuter ends of the leadsare connected, a pair of metal lugs secured to and extending outwardlyfrom the respective conductive members, means carried by and formingpart of the tube for connecting the filament to a source of powercomprising a pair of conductive elements of selected electricalresistance characteristics having one end interchangeably connected .tothe respective lugs, the elements being freely suspended from the lugs,and terminals on the other ends of the elements for connection toelectrical means external of the tube.

3. Avalve tube comprising a vacuum envelope having a reentrant portionat one end extending for a substantial distance into the envelope andforming a central cavity in that end of the tube exteriorly of thevacuumized portion of the envelope, a filament in the vacuumized portionof the envelope, a pair of relatively rigid supports connected withthefilament and extending outwardly of the envelope into the cavity, adielectric deck freely located on the end of the envelope and spanningthe cavity, a pair of electrically conductive members on the deck, meanscarried by and forming part of the tube forconnecting the filament to asource of power comprising a pair of conductive elements of selectedelectrical resistance characteristics having one end connected to therespective conductive members and freely suspended therefrom, and meansfor supporting the deck in position over said cavity comprising a pairof spaced flexible leads having one end connected to respectiveconductive members on the deck and having their other ends connected torespective supports, the connectors being relatively taut to preventdisplacement of the deck and of electrically conductive material tosupply electrical energy from said elements to the filament.

References Cited in the file of this patent UNITED STATES PATENTS

